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“Diogenes the Cynic also served as a slave, but he was a freeborn man, who was sold into slavery. When Xeniades of Corinth wished to buy him and asked whether he knew any trade, Diogenes replied: "I know how to govern free men."[n 1] Then Xeniades, in admiration of his answer, bought him, set him free, and entrusting to him his own children, said: "Take my children to govern."” — Aulus Gellius, Noctes Atticae, ii. 18.[1]

“I must tell you how wittily Diogenes paid back a sophism of that kind which I have mentioned above, proposed with insulting intent by a logician of the Platonic school. For when the logician had asked: "You are not what I am, are you?" and Diogenes had admitted it, he added: "But I am a man." And when Diogenes had assented to that also and the logician had concluded: "Then you are not a man," Diogenes retorted: "That is a lie, but if you want it to be true, begin your proposition with me."” —

↑The Latin word for free men and children is the same (liberi), but it seems impossible to reproduce the word play in English. For the story about the capture and sale of Diogenes, see Diogenes Laërtius, vi. 29-32, 36, 74-75.